It is known to provide an assembly comprising a crankshaft, connecting rod, gudgeon pin and piston for converting linear motion into rotary motion in an internal combustion engine. In a typical crankshaft arrangement, the crankshaft has one or more offset portions which are offset from the axis of rotation of the crankshaft, and the or each connecting rod is mounted for rotation about one of the offset portions. By means of the axes of rotation of the connecting rods being spaced from the axis of rotation of the crankshaft, pistons constrained within cylinders and mounted to free ends of the connecting rods move in reciprocating linear motion as the crankshaft rotates. Such an arrangement has the disadvantage of being limited to a symmetric cycle such that the piston moves at the same average velocity in the power (expansion) stroke as it does in the compression stroke. Moreover, typical arrangements of this type also have the disadvantage of the connecting rod being necessarily coupled to the piston by a pivotal coupling (commonly a pin) which experiences high stresses and is subject to wear and/or breakage.
Various alternative arrangements for connecting a reciprocating piston to a rotating crankshaft have also been proposed. One such arrangement is disclosed in U.S. Pat. No. 5,664,464 to Carson in which a piston is connected to a crankshaft by way of an offset crankpin 34 mounted through a cylindrical portion 40 which, in turn, is mounted for rotation within a reciprocating member assembly 10. However, this arrangement is also limited to a symmetric cycle in which the piston travels at the same average velocity in the power and compression strokes. Additionally, the device disclosed in this document is restricted to the offset of the crankpin 34 from the axis of the a being the same as the offset of the axis of the cylindrical portion 40 from the axis of the crankpin 34 which limits the geometry achievable for the cycle of the device.